Location-based technology is a technology of acquiring information about the physical, geographical, and logical locations of an object (a person or thing) placed at a specific location, and appropriately reacting according to the acquired information. The conventional positioning methods include a triangulation method of determining a location by measuring a difference of distances between objects, an angle between them, or an azimuth angle between them, a scene analysis method using a scene viewed from a specific vantage point, and a proximity method of finding an object by approaching a specific location.
Recently, with the development of wireless communication technologies, a radio frequency identification (RFID) system has been highlighted as new wireless network technology, and has been widely used. It has been required to develop a technology of measuring a location indoors or outdoors by using the RFID system, and such a technology can be utilized for various purposes, such as collecting data by means of RFID in an inaccessible area, transmitting the collected data to users, etc.
Meanwhile, conventionally, there are various location measurement technologies, including a location measurement technology using a global positioning system (GPS), a location measurement technology using a received signal strength indication (RSSI) of a radio frequency signal, a location measurement technology using local-area wireless communication, etc.
The location measurement technology using a GPS is a technology of measuring a distance to a GPS satellite, which orbits the earth, by measuring the phase of a carrier signal sent from the GPG satellite (i.e. by absolute positioning) or by tracking the code of the carrier signal (i.e. by relative positioning). Since the location measurement technology using a GPS has wide signal coverage, and can stably provide service through a fixed satellite, it is currently the most widely used. However, the location measurement technology using a GPS has disadvantages in that precision is low, and that service is unavailable in shadow areas or indoors where GPS satellite signals cannot be received.
The location measurement technology using mobile communication is a technology of obtaining information about the geographical location of a mobile terminal through the triangulation method using a mobile communication system which has been constructed. The location measurement technology using mobile communication includes a network-based scheme of finding the location of a terminal through cooperation between a base station of a serving cell of the terminal and a neighboring base station, a terminal-based scheme in which a terminal having a GPS receiver, separately from a base station, transmits location information to a network, and a mixed scheme in which the two schemes are combined. These technologies do not require a separate infrastructure, and have wide service coverage, similar to the GPS, thereby being widely utilized as a macro-positioning technology. However, the technologies have a disadvantage in that the technologies can be used only within a cell radius around a base station and in metropolitan areas where radio waves can be received, and accuracy is degraded indoors due to diffraction by propagation characteristics, multiple paths, and signal attenuation.
The location awareness technologies using the satellite communication or mobile communication are suitable for an outdoor environment because of wide service coverage, but the location awareness technologies are restricted in shadow areas or indoors. Therefore, recently, research is being actively conducted into positioning methods using various wireless communication technologies, such as diffuse-infrared, ultrasonic wave, radio frequency (RF), ultra wideband (UWB), and radio frequency identification.